Galvanizing continuous elements with prevention of corrosion of the pan

ABSTRACT

A METHOD AND APPARATUS FOR GALVANTIZING STEEL WIRE INCLUDING A CORRODIBLE ELECTRICALLY CONDUCTIVE PAN CONTAINING A ZINC BATH THROUGH WHICH THE WIRE IS MOVED LENGTHWISE AND IN WHICH THE WIRE IS BROUGHT TO TEMPERATURE SUBSTANTIALLY ABOVE THE INVERSION TEMPERATURE WITH ZINC WITHIN THE BATH, THEREBY CREATING CURRENT FLOW TOWARD BOTH THE INLET AND OUTLET ENDS OF THE BATH WITHIN THE WIRE. THE METHOD AND APPARATUS INVOLVES THE USE OF SEPARATE SHORT CIRCUITS INCLUDING A FIRST SHORT BETWEEN THE WIRE AT THE ENTRY END OF THE BATH AND THE WIRE AT APPROXIMATELY ITS POSITION OF INVERSION TEMPERATURE WITHIN THE BATH AND A SECOND SHORT BETWEEN THE WIRED AND THE FIRST AND SECOND INTERMEDIATE SINKERS, THEIR POSITION BEING AT MAXIMUM WIRE POTENTIAL IN THE BATH BEYOND THE INVERSION TEMPERATURE POSITION. BOTH OF THE SHORT CIRCULTS ARE ELECTRICALLY INSULATED FROM THE PAN, THEREBY ELIMINATING ANY CORROSION-INDUCING CURRENT FLOW THROUGH THE PAN. THE SECOND SHORT CIRCULT ALSO ASSURES AN EVEN POTENTIAL IN THE WIRE OVER A SIGNIFICANT LENGTH OF THE BATH TO ASSURE PRODUCTION OF AN EVEN COATING ON THE WIRE. THE BATH INCLUDES AN ENTRY SINKER BAR WHICH IS ELECTRICALLY CONDUCTIVE AND FORMS A PORTION OF THE FIRST SHORT CIRCUIT AND TWO INTERMEDIATE SINKER BARS WHICH FORM A PORTION OF THE SECOND SHORT CIRCULT. THE FIRST SINKER BAR IS POSITIONED AT APPROXIMATELY THE POSITION OF INVERSION TEMPERATURE WITHIN THE BATH AND THE INTERMEDIATE SINKER BAR ARE POSITIONED AT APPROXIMATELY THE POSITION OF MAXIMUM POTENTIAL ABOVE THE INVERSION TEMPERATURE POSITION. THE INTERMEDIATE SINKER BARS ARE SLIGHTLY LOWER IN THE BATH THAN THE OTHER TWO BARS TO ASSURE ELECTRICAL CONTACT OF THE WIRE THEREWITH. WIRES OF ANY GAUGE CAN BE GALVANIZED IN THE SAME BATH SIMPLY BY REGULATING THEIR IMMERSION TIME IN THE BATH TO ASSURE THE DESIRED COATING WEIGHT.

BROWN 3,684,563

ELEMENTS WITH PREVENTION 2 Sheets-Sheet 1 Aug. 15, w H. GALVANIZINGCONTINUOUS OF CORROSION OF THE PAN Filed Jan. 14, 1971 F KGV v V Aug.15, w, BROWN 3,684,563

GALVANIZING CONTINUOUS ELEMENTS WITH PREVENTION OF CORROSION OF THE PANFiled Jan. 14, 1971 2 Sheets-Sheet 2 I I I I I 5 00 6'00 750 8150 9'00la'oo 40 0 o TEMPE/PA 70/?5 C I a I Q QmaII United States Patent Office3,684,563 Patented Aug. 15, 1972 r 3,684,563 GALVANIZING CONTINUOUSELEMENTS WITH PREVENTION OF CORROSION OF THE PAN William H. Brown, 6200S. Adams St.,

Barton'ville, II]. 61607 Filed Jan. 14, 1971, Ser. No. 106,442 Int. Cl.C23c 1/02 US. Cl. 117-114 A 9 Claims ABSTRACT OF THE DISCLOSURE A methodand apparatus for galvanizing steel wire including a corrodibleelectrically conductive pan containing a zinc bath through which thewire is moved lengthwise and in which the wire is brought to atemperature substantially above the inversion temperature with zincwithin the bath, thereby creating current flow toward both the inlet andoutlet ends of the bath within the wire. The method and apparatusinvolves the use of separate short circuits including a first shortbetween the wire at the entry end of the bath and the wire atapproximately its position of inversion temperature within the bath anda second short between the wires and the first and second intermediatesinkers, their position being at maximum wire potential in the bathbeyond the inversion temperature position. Both of the short circuitsare electrically insulated from the pan, thereby eliminating anycorrosion-inducing current flow through the pan. The second shortcircuit also assures an even potential in the wire over a significantlength of the bath to assure'production of an even coating on the wire.

The bath includes an entry sinker bar which is electrically conductiveand forms a portion of the first short circuit and two intermediatesinker bars which form a portion of the second short circuit. The firstsinker bar is positioned at approximately the position of inversiontemperature within the bath and the intermediate sinker bar arepositioned at approximately the position of maximum potential above theinversion temperature position. The intermediate sinker bars areslightly lower in the bath than the other two bars to assure electricalcontact of the wire therewith. Wires of any gauge can be galvanized inthe same bath simply by regulating their immersion time in the bath toassure the desired coating weight.

BACKGROUND OF THE INVENTION Field of the invention I Brief descriptionof the prior art It is a usual practice to galvanize a continuouselement, such as a steel wire, by drawing the element from a sourcethrough a pan containing molten zinc to a take-up reel. A seriouspractical problem is the short life of the pan which tends" to erode andfail, generally in the vincinity of the point of entry of the wire,usually after an average of only six to eight months. However, they havefailed in thirty days.

I believe that pan erosion is caused by an electrochemical reactionresulting from a flow of electric current between the wire, the zinc andthe pan.'The current flow is established by thermoelectric potentialsdeveloped along the length of the wire as a resultof temperaturediflerentials encountered in the galvanizing operation. Briefly, twotypes of potentials are present: (1) the potential resulting from theabsolute temperature of the wire itself (the Thompson effect), and (2)the potential resulting from the temperature difference between thesteel wire and the molten material in which it is immersed (the Seebookeffect). The potentials due to the latter effect are of greatersignificance with respect to pan erosion.

In addition to pan erosion, current continuous galvaizing systems sufferother drawbacks which hamper production and decrease production rates.For example, the coatings vary over a wide range, requiring operating atreduced speeds to minimize the coatings below specifications. Also, thevariations in coatings increase the zinc consumed per ton of wire, thusincreasing the zinc cost by several dollars per ton of wire. Also, attime rejects due to low coating are high. In some cases, the coatingthickness varies more than on samples taken from a single strand ofwire.

SUMMARY OF THE INVENTION This invention provides a method and apparatusfor galvanizing an elongated conductive metal element by moving theelement lengthwise through a molten zinc bath contained in a corrodiblecontainer while blocking the flow of electric currents through thecontainer, thereby inhibiting corrosion.

In a preferred form, the method and apparatus is capable of galvanizingsteel wire moved through the bath on a generally continuous basis. Inthe preferred bath container, the incoming sinker is located atapproximately the position at which the wire reaches the inversiontemperature with the zinc in the bath and the intermediate sinkers areprovided between the incoming sinker and the exit sinker atapproximately the position where the wires reach maximum potentialbeyond the inversion temperature within the bath. In this form, twoshort-circuits are provided, one shorting the potential in the wiresbetween incoming sinkeror position of inversion temperature with thewire prior to entry into the bath, and a second which shorts anypotential dilferences in the wires between the intermediate sinkers.Both of the Short-circuits are electrically insulated from directcontact with the bath container. t

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will be described herein indetail, a specific embodiment of the invention with the understandingthat the invention is not intended to be limited to such embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a molten zincbath useful in the method of the present invention;

FIG. 2 is a longitudinal section along line 22 of FIG. 1;

FIG. 3 is a section along line 3-3 of FIG. 2;

FIG. 4 is an enlarged section along line 4-4 of FIG. 1;

FIG. 5 is a plot of thermoelectric powers useful in understanding thepresent invention; and

FIG. 6 is a longitudinal section reduced from FIG. 2.

DEVELOPMENT OF BACKGROUND MATERIAL AND STUDY OF THE PROBLEMS SOLVED BYTHE INVENTION [The present invention is the result of a new approach tosolving the problems of pan erosion, dross formation and uneven coatingsin galvanizing wire. Following my belief that pan erosion results fromflow of electric currents through the bath and pan, I have studied thepatterns of current show through a galvanizing system. For

purposes of the following explanation of the background and the problemconsider a molten zinc bath somewhat like that shown in FIG. 2 but inwhich the entry wire support bar 12 and exit drip bar or wiper 14 aremounted out of direct electrical contact with the pan 16, incomingsinker 18 and exit sinker 20 are secured by upstanding support arms inelectrical contact with flange lip 22 of pan 16. And sinker bars 24 and26 and contacts 28 and 30 are eliminated. Pan 16 contains a bath 32 ofmolten zinc at the normal process temperatures of about 460 C.

In a conventional galvanizing operation, the wire is drawn from a sourcesuch as a reel through an acid bath to clean the wire and then through adrying oven. From the drying oven the Wire is drawn through thegalvanizing bath, then in some cases through an annealing furnace atabout 1000 F. and is then wound on a take-up reel. The method iscontinuous to the extent that an entire reel of 'wire is drawn throughthe complete galvanizing system and is taken up as galvanized wire onthe take-up reel. The method continuously processes each reel of wireand during its travel through the system the wire passes across varioussupports and beneath sinkers in the various baths.

As shown in FIGS. 1 and 2, the wire 10 enters and passes through thegalvanizing bath and is kept submerged in the bath by an incoming sinker18 and an exit sinker 20. Plural wires may be processed at one time andthe separate wires 10a, 10b, 10c, 10d, etc. can be recovered on separatetake-up reels.

The steel wire elongated element 10 is a conductor and in a typicalgalvanizing apparatus, the wire is passed beneath the sinkers 18 and 20which hold the wire submerged in the galvanizing bath. In prior systems,the sinkers were conductive elements mounted on the conductive flangesof the pan.

During the course of the galvanizing operation the temperature of thewire changes radically. Prior to entering the galvanizing bath the wireis at about ambient temperature and in the galvanizing bath the wire isheated to a temperature on the order of 460 C., i.e., the temperature ofthe molten zinc. The temperature variations along the length of the wireduring heating within the galvanizing bath establish thermoelectricpotentials in the wire. Referring to FIG. 2 of the drawing, if apotential reading is taken from a wire between point B at the incomingend of the zinc bath and point F at the exit of the bath, it isdiscovered that the potential not only varies over a wide range but attimes the potential even reverses. I have found that when the exit endof the wire is positive in polarity, a potential in excess of twomillivolts is often created and when the incoming end is positive, apotential in excess of one millivolt is often created. The potentialvaries between these limits, constantly changing or drifting up or down.

As an example of the variances in potential, I took potential readingsfrom seven wires being run on a twenty-four wire frame over atwenty-four hour period, and the variance in these readings is givenbelow:

Potential variance Wire No. I in millivolts '1 .3 to .3

The relative magnitudes of the Seebook effect potentials are illustratedin FIG. 5. Where experimentally determined, thermoelectric powers foriron and zinc are plotted. The voltage which is developed as a result ofa temperature difference between the junctions of the two dissimilarmetals forming a potential depends on three factors: (1) the metals; (2)the difference of temperature between the junctions; and (3) the meantemperature of the two junctions. In a galvanizing process where amaterial is submerged in'a hot bath of another material there are both ajunction and a temperature differential over an extended length and thesystem is not susceptible of a simple quantitative analysis. However, aconsideration of FIG. 5 will aid in a qualitative understanding of theproblem. If, for example, there is a circuit of iron and zinc with onejunction at 300 C. and the other junction at 400 C., the meantemperature is 350 C. and with references to FIG. 5, the thermoelectricpotential difference is about 11 microvolts per degree. Since thetemperature differential is C., the generated voltage is about 1.1 ofmillivolts. Where the plots for iron and zinc cross at about 237 C., thepolarity of the voltage developed in one portion of the system is theopposite of that in the other and the net voltage is the differencebetween the two. The point of intersection between the two is a neutraltemperature or point of inversion for the two materials. If thistemperature is the mean of the temperatures of the two junctions, no netvoltage is generated.

Considering the inversion temperature of 237 C. in FIG. 5 as point X inthe galvanizing bath of FIGS. 1 and 2, the potential X-B in the wireincreases from point X to point B, or cold end of the wire. Anotherpotential X-F in the wire increases in the opposite direction from pointX to point P, or the high temperature end. Thus, in FIG. 2, currentflows from point X toward both ends of the wire 10. Assuming that boththe incoming sinker 18 and exit sinker 20 in the system of FIG. 2 arebolted in electrical contact to the flange 22 at the top of the pan 16,the following circuit is created: the wire 10 makes contact with theexit sinker 20 and through the exit sinker 20 to the pan flange 22, thenthrough the pan sides and flange back to the ends of the incoming sinker18 through the incoming sinker 18 to the wire 10 and then through thewire 10 into the exit sinker 20. This forms a complete circuit.

Returning to FIG. 5, it will be noted that there is a potential from thewire to the zinc coating when the temperature of the wire is equal tothe temperature of the zinc bath, or 460 C. This potential difference ison the order of 20 microvolts. Additionally, when the sinkers have azinc coating at the point of contact with the wire, the sinkers have anequal potential but the direction of the sinker potential is from thesinker to the wire. If the exit sinker 20 is coated at the point ofcontact with the coated wire 10, there are two opposing potentials atthis junction.

At the incoming end of the bath, the incoming wire, being at aboutambient temperature, lowers the temperature of a thin cover of zinc incontact with the wire for a short time. If it is assumed that thetemperatures of the incoming wire and its coating have increased to theneutral inversion point, i.e., 237 C., by the time it reaches theincoming coated sinker 18, the potential between the wire and its zincjacket is momentarily zero. But since the sinker 18 is coated at thepoint of contact of the wire, the potential of the sinker at bathtemperature is from the sinker to the wire. The direction of thispotential is the same as the *X-B and X-F potentials so that thepotential from the incoming sinker is added to the X-B and X-Fpotentials. If no current flows in the wire to reduce its potential, thepotential from the incoming sinker 18 and the X-F potential will remainsteady at a maximum value, resulting in a maximum uniform coating.However, the potential generally results in a current flow through thewire to the exit sinker 20 and through the circuit described above.

As indicated above, the X-B potential is developed in the incoming wirefrom a point near the incoming sinker to the point of initial contact ofthe wire with the molten zinc bath. The current from this potentialflows in the wire toward the point of contact with the zinc bath, thenthrough the zinc bath to the incoming end of the pan or the sides of thepan near the incoming corners, then through the end of the pan to thesides of the pan and back toward the end of the incoming sinker 18. Inthe absence of any interference, the current would continue to flowthrough the pan sides and flanges to the ends of the incoming sinker 18and through the sinker back to the wire, completing the circuit.However, the ends of the incoming sinker normally have a potential equalto or greater than the X-B potential because of the X-F potentialdescribed above. This forces the returning cur rent resulting from theX-B' potential to flow through the sides of the pan, near the ends ofthe incoming sinker and the zinc bath, back to the wire. If theresistance in the connection between the flange 22 of pan 16 and one orboth ends of the incoming sinker 18 is high, some of the currentresulting from the X-F potential is forced to flow through the side ofthe pan 16 near the ends of the incoming sinker 18 and the zinc bath 32back to the wire 10. It is my belief that any current flowing throughthe sides of the pan to the bath reduces the life of the pan by causingcorrosion or pitting.

The current flowing from the zinc-coated wire to the exit sinkerdeposits some of the zinc from the wire onto the exit sinker. As thezinc deposit builds up on the exit sinker, the opposing potential fromthe sinker increases, also the contact resistance, thereby reducing thecurent flow and increasing the X-F potential in the wire, also itscoating. Thus, during the galvanizing operation the potentialcontinuously varies and the thickness of coatings on the wire alsonormally varies.

As another consideration, it is often desirable to run a galvanizingunit using several different sizes of wires simultaneously, e.g., at10a, 10b, etc. Also, at times, coating specifications may requirerunning some of the wires at different speeds from other wires ofdifferent size. This creates poor conditions for forming uniformcoatings because the resistance of different sizes of wire are not equaland the small wires come up to bath temperature and maximum potential inless time than the larger wires. Each of the wires being in contact withthe incoming and exit sinkers and having maximum potentials at differentpositions in the bath causes circulating currents to flow between thedifferent wires through the bath and sinkers. These circulating currentscause potential variations in the different size wires, resulting invariations in coating thickness. The range of coating variations is highin conventional galvanizing processes.

Variations in tension of the wires passing through the bath also causecoating variations. When the contact pressure between the wires and thesinkers increases, reducing the resistance of the contacts andincreasing the current flow in the circuit, the X-F potential and thecoating is reduced. Such variations in wire tension can result fromvariations in amounts of wire on the reels, the breaking effect of thereel breaks which are not always uniform, increased friction due toright angle turns in some of the wires before entering the galvanizingbath, and non-uniform take-up on the take-up reels, which often causesthe reels to speed up or slow down, thereby changing the tension in thewires.

There are other factors contributing to variations in the potential andthe current flow. Since the wire is under tension as it is being movedthrough the bath, a considerable amount of friction results between thewire and the sinkers and the friction wears through the zinc coating onthe sinkers. As the'sinker coating wears thin, the opposing potentialfrom exit sinker 20 is reduced. This increases the current flow betweenthe wire and the sinker and as a result of the current flow in thecircuit, the potential of the source is reduced. The potential drop inthe wire is equal to the current in amperes times the internalresistance of the potential source in ohms and in a galvanizing bath theresistance of the potential source, i.e., the hot wire between thesinkers, is quite high so that a large drop in the X-F potential resultswith a relatively small current flow. Thus, as the current in thecircuit increases the XF potential drops and the current will increaseuntil the potential drops to a value at which it cannot force any morecurrent through the resistance of the circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The form of the inventionillustrated in the drawings is especially adapted to galvanizing steelwire which is drawn from a reel through the galvanizing process andcoiled on a take-up reel. It is applicable not only to wire, but tostrips and webs of other configurations. Further, it is not essential tothe practice of the invention that the material to be galvanized bedrawn from a reel or roll. For example, the wire can come directly froma wire-drawing die. Similarly, it is not necessary that the galvanizedwire be wound on a take-up reel. It can be cut into short lengths andstacked, for example.

The embodiment shown in FIGS. 1-4 and 6 diifers from a conventionalgalvanizing process. Accordingly, the incoming wire support bar 12 iselectrically connected to the incoming sinker 18 by a pair of electriccontact bars 28 secured to the ends of bar 12 and the ends of theincoming sinker 18. Also, sinkers 24- and 26 are provided atapproximately the position of the maximum value of the X-F potential andthe ends of sinkers 24 and 26 are secured to and in electrical contactwith a second pair of electric contact bars 30 to which the ends of exitsinker 20 are also secured and on which the exit drip bar or wiper 14 ismounted so that bars 30 assure electric contact between sinkers 20 and24 and 26 and wiper 14. The zinc bath and pan 16 is completely insulatedfrom ground at all times during the operation of the apparatus.

The electric contact bars 28 and 30 are supported by and secured to theedge flange of pan 16 via electrically insulating mounting means 40. Asbest seen in FIG. 4, each insulating mounting means 40 includes a nut 42welded to the top of flange 22. Insulating washers 44 and 46 and anintermediate insulating sleeve 48 are positioned in. a base in contactbar 28 or 30 on top of the nut 42 as shown. A bolt 50 extends throughthe washers 44 and 46 and the sleeve 48 and is threaded into the nut 42.Washers 44 and 46, respectively, underlie and overlie the bar 28 or 30and, with sleeve 48, completely insulate the bar 28 or 30 from the bolt50, nut 42 and flange 22. Between the head of bolt 50 and the overlyinginsulating washer 46 there is provided a metal washer 52 which helpsclamp washers 44 and 46 more securely against the faces of bar 28 or 30.

Each insulating mounting means 40 also includes a protective coversystem for protecting the insulated connection. Accordingly, acylindrical skirt 54 is provided welded to the bottom of bar 28 or 30surrounding the nut 42 and spaced outwardly from the nut 42. The skirt54 stops short of flange 22 to assure that no electrical contact is madebetween the protective cover and flange 22. Welded to the top of eachbar 28 or 30 and around the bore is an upstanding cylindrical wall 56.Wall 56 surrounds but does not contact washer 52. The cylindrical wall56 has external threads which receive a removable cap 58. The removablecap 58 permits easy access to the bolt 50 for tightening or looseningthe mounting as desired.

In effect the contact bars 28 provide a low resistance short circuitacross the X-B potential so that the potential is reduced to a very lowvalue. This very low value results from the low resistance of a shortpiece of wire included in the circuit and the lower average temperatureof the short piece of Wire. The contact bar 12 'being connected at eachend to the bars 28 complete a circuit from the incoming wires to thecontact bar, through the contact bar and the end connections to the endsof the incoming sinker 18 and through the incoming sinker 18 back to thewire 10, thus shorting the X-B potential. The shorting entry barincluding the end connections and incoming sinker are all electricallyinsulated from pan 16 as a unit so that the X43 potential is reduced toa very low value and any possible current resulting from the X-Bpotential is prevented from flowing from the wire to the zinc bath thento the pan or from the pan into the zinc bath.

As described above, the ends of the exit sinker are mounted on bars 30which are electrically insulated from the pan. This opens the circuitinvolving the X-F potential and prevents current from flowing throughthe sides of the pan, then through the zinc bath to the wire. Thus, thecircuit described above with regard to X-F potential is broken and,since no current flows, the X-F potential remains at a higher averagevalue. The higher average X-F potential in the wire results in a moreuniform coating on the wire than when the exit sinker is electricallyconnected to the pan.

The sinkers 24 and 26 further assure the formation of uniform coating onthe wires, even Where wires of different size are simultaneouslyprocessed. As described above, sinkers 24 and 26 are insulated from thepan in the same manner as the other sinkers. Further, the sinkers 24 and26 are spaced a distance from the incoming sinker 18 and are at a pointalong the bath where the XF potentials in all of the Wires haveincreased to the maximum value. For example, it requires approximately3% seconds for a #9 wire to come up to bath temperature and maximum X-Fpotential and assuming this is the thickest wire to be processed, theintermediate sinkers 24 and 26 can be located at that point in the bathwhere the wire is at bath temperature when operating at maximum speed toobtain the required coating.

The angle of the wire making contact with the incoming sinker 18, alsoleaving exit sinker 20 is quite large resulting in increased contactpressure and low resistance connections. The angle of the wire makingcontact with sinker 24 is very small. This reduces the contact pressureand increases the contact resistance. The addition of sinker 26 with theends of both sinkers 24 and 26 connected to conductors 30 results in thefollowing. This forms two circuits in parallel reducing the contactresistance by 50% Also, any variation in the wire potentials leavingsinker 24 are balanced by current circulating between the two sinkers inthe end connecting conductors 30. This increases the stability of thepotentials between sinkers 26 and 20, also the coatings.

It is believed that during galvanizing of wire using the presentinvention, the wire entering the molten zinc bath is covered with a thinlayer of zinc and the zinc temperature at the wire is reduced by thecooler wire. As the wire travels further through the bath the wiretemperature increases to bonding temperature and the zinc forms a bondon the wire. In the conventional process at times a large current causedby the X-F potential flows through the sides of the pan and the zinc tothe wire at the beginning of the galvanizing bath. This current depositsa thick jacket of zinc on the wire. The heavy jacket of zinc deters thetemperature rise in the wire so that the wire reaches the exit of thebath before its temperature is high enough to form a bond with the zinc,resulting in wire which must be scrapped. The present method eliminatesthe current flow to the wire at the incoming end of the bath, permittingthe very thin cover of zinc on the wire to form and permitting the wireto heat to bonding temperature in less time. This assures good bonds atall times and leaves a greater percentage of immersion time for coating.The method thereby practically eliminates scrap, and it stablizes thecoating time and the coating weight.

A major advantage of the invention is that it increases the life of thegalvanizing bath pan. Working with the 8 system has demonstrated thatpan life may be increased from a few weeks or months to approximatelythat of the pans used when the hot dip method is applied. The potentialdifferences do not occur with this method and the pans often last fromtwelve to fifteen years. In one instance a pan was operated by a priorart process for about ten days and it was found that several pitsdeveloped in the bottom of the pan up to inch in depth. For severalyears the pans on this frame had failed every five to seven weeks, withan average of less than six weeks. After then using the pan andoperating under the present invention for a period of 4 weeks it wasfound that all of the pits had filled up with zinc. The pan was still inoperation seven months later with no failure indicated. The extendedlife results in savings in material and down time.

Because of the uniform potential at maximum value in the coating area ofthe present invention, the system can be operated at a faster rate withassurance that the minimum specified coating thickness is formedthroughout the length of the wire. This has resulted in a productionincrease of about 35%. If the heating capacity or the take-up framelimits the speed, shorter pans can be used, resulting in less cost.Operating at maximum speed increases the wire tension and improves thecontact between the wires and the sinkers. This improves the voltagecontrol and reduces the coating variations. Increasing the operatingspeed reduces the immersion time and the coating weight. The optimumspeed is the maximum speed below the required immersion time to assurethe coating specifications.

Formation of dross is also reduced by about one-half because of theinsulating of the circuits and blocking flowage of current through thepan. Dress is believed to result from a current flowing from either thesteel wire or a steel pan into the zinc bath, causing disintegration ofsmall particles of the steel. These particles of steel unite with thezinc to form the dross and the dross settles to the bottom of the panand must be removed fairly frequently. The reduction of doss with thepresent invention results in saving of labor, down time and zinc whichwould otherwise be consumed in the dross.

I claim:

1. In a method of galvanizing an elongated conductive metal element bymoving the element lengthwise through a bath of molten zinc from anentry end to an exit end of the bath whereby the element is heated bythe molten Zinc within the bath beyond its inversion temperature withzinc so that current flows along the element toward both the entry andexit ends of the bath, the improvement comprising short-circuiting theentry end of said element with the portion of said element which is atabout the inversion temperature.

2. The method of claim 1 wherein said bath is contained in anelectrically conductive corrodible container and said short-circuitingis by means electrically insulated from said container.

3. The method of claim 2 including the step of maintaining the portionof said element which has left the bath at the exit end out ofelectrical contact with the container.

4. The method of claim 3 including the step of providing a stabilizedpotential in the element between the portion of the element at the exitend of the bath and the portion of the element within the bath which isat approximately maximum potential, above the inversion temperature andmoving toward the exit end of the bath.

5. The method of claim 1 including the step of maintaining the portionof said element which has left the bath at the exit end out ofelectrical contact with the container.

6. The method of claim 5 including the step of providing more constantpotential in the element between the portion of the element at the exitend of the bath and'the portion of the element within the bath whichis'at approximately maximum potential, above the inversion temperatureand moving toward the exit end of the bath, thereby providing a coatingof more uniform thickness on the element.

7. The method of claim 1 adapted for operation in galvanizing elementsof dilferent cross-sectional areas and which are heated to inversiontemperature by the bath at difierent rates, wherein a fixed inversiontemperature position is provided for all elements moving through thebath in which said moving step comprises delivering the elements throughthe bath at a rate assuring that all of the elements are at inversiontemperature at said position of inversion temperature.

8. The method of claim 1 wherein said element is steel wire of generallyuniform diameter over its length which is moved as a generallycontinuous strand through the galvanizing bath.

9. The method of claim 8 wherein said element comprises a plurality ofparallel strands of wire which are moved as separate generallycontinuous strands through the bath.

1 0 References Cited UNITED STATES PATENTS Re. 12,779 4/1908 Goodson117-93 X 1,053,664 2/1913 Sommer 117-114 A 1,872,712 8/1932 Fahrenwald118-429 X 1,890,463 12/1932 Herman 117-114 A 2,063,721 12/1936 Bradley117-14 A UX 2,286,194 6/ 1942 Bradley -117-93 X 2,405,222 8/1946 Mann117-114 R X 2,744,495 5/ 1956 Boegehold 118-429 FOREIGN PATENTS 18,9107/ 1907 Great Britain 117-128 ALFRED L. LEAVI'IT, Primary Examiner I. R.BA'ITEN, JR., Assistant Examiner U.S. Cl. X.R.

